\documentclass[10pt]{article} % required
\pagestyle{empty} % required
\usepackage{amsmath}
\usepackage{amssymb}
\usepackage{color}
\usepackage[T1]{fontenc}

\begin{document}\definecolor{fgC}{rgb}{0,0,0}\color{fgC}\[\begin{matrix}
  U_t = R(U)  \Leftrightarrow U_t = F(U)_x \\
  U = [u]\;\;\;
  F(U) = [-\frac{1}{2}u^2+\nu u_x]
\end{matrix}\]\end{document}